1. Field of the Invention
The present invention is directed to a computer tomography apparatus of the type having a coaxially disposed annular anode, detector ring and cathode ring.
2. Description of the Prior Art
Computer tomography systems are known in the art having an annular anode, a detector ring surrounded by the anode and a cathode ring, with the annular anode, the detector ring and the cathode ring being coaxially disposed. The cathode ring consists of a series of cathodes whose respective electron emission to the anode is enabled from cathode-to-cathode so that the focus from which x-rays are emitted by the anode is shifted step-by-step.
In a computer tomography systems of this type, the anode, the detector ring and the cathode ring are stationary while the examination subject is being scanned by a fan-shaped x-ray beam from various angles. Consequently, an extremely fast scanning of the examination subject through a total angle of 360.degree. is possible. The image registration time, therefore, can be extremely short.
Because the individual cathodes of the cathode ring have a finite width, the number of cathodes employable in the cathode ring, and thus the number of possible focus positions, is limited. Given a center-to-center spacing of the cathodes of, for example, 4 mm, only approximately one-thousand focus positions can be accommodated on the anode having a standard circumference of approximately 4 meters. The center-to-center spacing of the cathodes cannot be arbitrarily reduced in order to increase the number of possible focus positions.